2.1.4.3.8.1 DTD syntax specialization module coding requirements

To be extensible and backward compatible, DITA requires that a DTD implementation of
structural and domain specialization modules conform to well-defined implementation (coding)
requirements.

These coding requirements implement the specialization architecture with the capabilities and
within the limitations of the DTD grammar. They are the coding requirements for structural
specializations, element domain specializations, and attribute domain specializations.

2.1.4.3.8.1.2 Structural module coding requirements
A structural vocabulary module defines a new topic or map type as a specialization of a base topic or map type. The purpose is usually to enhance the user's interaction by adapting the topic or map type to its particular purposes.

2.1.4.3.8.1.4 Element domain module coding requirements
An element domain vocabulary module defines element types that are appropriate for the subject-matter or application domain for which they are designed. The purpose is usually to enhance the user's interaction by providing "semantic" elements whose names more accurately denote their content, making that content easier to search and retrieve.